Image readers that transfer a plurality of mediums placed on a hopper one by one, and read images on the mediums have been known (refer to Japanese Laid-open Patent Publication No. 2003-81512).
This kind of image readers are enabled to transfer mediums appropriately one by one when the mediums are placed on a hopper with the edges aligned, and to read images on the mediums appropriately. Therefore, users make sure that the edges of the mediums are aligned, and then put the mediums on the hopper. This type of medium transfer device is disadvantageous in that mediums are not appropriately transferred one by one when the mediums are put on the hopper without aligning the edges, and images on the mediums are not appropriately read.